In a disk drive, a magnetic recording head is made of read and write elements. The write element is used to record and erase data bits arranged in circular tracks on the disk while the read element plays back a recorded magnetic signal. The magnetic recording head is mounted on a slider which is connected to a suspension arm, the suspension arm urging the slider toward a magnetic storage disk. When the disk is rotated the slider flies above the surface of the disk on a cushion of air which is generated by the rotating disk.
Write heads for disk or tape drives commonly include Permalloy (approximately 80% Ni and 20% Fe), which is formed in thin layers to create magnetic features. For example, an inductive head may have conductive coils that induce a magnetic flux in an adjacent Permalloy core, that flux employed to magnetize a portion or bit of an adjacent media. That same inductive head may read signals from the media by bringing the core near the magnetized media portion so that the flux from the media portion induces a flux in the core, the changing flux in the core inducing an electric current in the coils. Alternatively, instead of inductively sensing media fields, magnetoresistive (MR) sensors or merged heads that include MR sensors may use thinner layers of Permalloy to read signals, by sensing a change in electrical resistance of the MR sensor that is caused by the magnetic signal.
In order to store more information in smaller spaces, transducer elements have decreased in size for many years. One difficulty with this deceased size is that the amount of flux that needs to be transmitted may saturate elements such as magnetic pole layers, which becomes particularly troublesome when ends of the pole layers closest to the media, commonly termed poletips, are saturated. Magnetic saturation in this case limits the amount of flux that is transmitted through the poletips, limiting writing or reading of signals. Moreover, such saturation may blur that writing or reading, as the flux may be evenly dispersed over an entire poletip instead of being focused in a corner that has relatively high flux density. For these reasons the use of high magnetic moment materials in magnetic core elements has been known for many years to be desirable.
In order to write to higher coercivity media, which is more stable once written to, materials with higher magnetization are required to produce the necessary higher flux density. High magnetic moment materials allow application of higher flux density or higher field into the media, and thus enable writing to media having higher coercivity. High magnetic moment materials also allow the head to write a smaller bit, i.e., to write a higher bit density per length of track.
Iron is known to have a higher magnetic moment than nickel, so increasing the proportion of iron compared to nickel generally yields a higher moment alloy. Iron, however, is also more corrosive than nickel, which imposes a limit to the concentration of iron that is feasible. Also, it is difficult to achieve soft magnetic properties for iron-rich NiFe compared to nickel-rich NiFe. Nitrogen or nickel can be added to NiFe to reduce the magnetic hardness of the film, but the addition of these elements can dilute the magnetic moment significantly.
NiFe (80/20 Permalloy) is known to have a magnetization of 10 kGauss. CoFe alloys are known to a have a much higher magnetic moment, with a magnetization of about 24 kGauss. However, CoFe has only recently gained popularity as a construction material because it is magnetically hard, i.e., has a high coercivity so it requires a high magnetic field to switch direction. CoFe is also prone to corrosion.
What is needed is a CoFe based film which takes advantage of the high magnetization properties of CoFe, but which is also magnetically soft and therefore does not need a high current through the coils to switch the writer.
What is further needed is a CoFe based film which resists corrosion.